A saw has come to be one of the most commonly used tools for construction and structural fabrication. Because of their ease of use and versatility, power driven circular saws have gained widespread acceptance for wood framing and similar applications. Power driven circular saws are available in many sizes ranging from heavy, fixed installations such as radial arm saws or table saws to relatively light weight hand held portable saws.
While portable saws are convenient because of their light weight, they are also difficult to use. Their very portability makes it difficult to obtain an accurately positioned, precision straight line cut. Often times years of experience are required before a worker can made fast, accurate cuts on a rotatable basis using a portable saw. However, hiring highly experienced workers to operate a power saw adds substantially to construction costs. Frequently less experienced workers are used and the result is often lower quality workmanship which may produce a finished product that is either esthetically or structurally flawed. Portable saws are also prone to experience a kickback or violent jerking motion if a saw cut is not maintained prefectly straight. This particularly becomes a problem when the wood being cut is not completely dry.
For these reasons it is common for a construction contractor to establish a fixed sawing center for use at a construction project. This facilitates good quality cuts with less experienced labor but increases material handling costs. When delivered, the wood must be unloaded and stacked near the sawing center. It must then be moved to a position next to a saw, sawed and stacked. It must then be moved again to a location at which it is to be finally used. Invariably some of the wood is sawed to an incorrect length or routed to a wrong final assembly location. This not only necessitates additional handling but may idle skilled workers and slow construction while correct replacement materials are obtained.
A pressing need thus exists for an accurate, light weight, self guiding portable saw that would enable an inexperienced user to make fast but accurate cuts. Such a saw could be advantageously used as either a primary sawing tool or as a custom fitting supplement to a fixed position sawing center.
Many attempts have been made to produce a self guiding portable saw. However, because of high manufacturing costs, difficulty of use, excessive weight or other reasons, these self guiding saws have not achieved widespread popularity.
U.S. Pat. No. 4,335,512 to Sheps et al discloses a dual slide arrangement having two telescoping ball bearing connected slides. The slides have rounded bearing engaging surfaces which produce an arc of engagement and hence entrapment of sawdust with a consequent tendency to clog the track. Stops are located centrally of the inner slide relative to the outer slide. The alignment mechanism or fence 63 hasa not horizontal member extending over the workpiece. It thus cannot be accurately and securely clamped to the workpiece by hand, making it difficult to use the saw guide with a relatively narrow workpiece such as a 2.times.4. Furthermore, when retracted, the saw travels back over the guide member, further interfering with manual securing of the guide mechanism to the workpiece.
U.S. Pat. No. 3,991,643 to Girardin shows a guide arrangement with a slide which is extendable over a substantial distance in each direction. However, the slide is not bearing mounted to the track and the cut is made with the saw being drawn toward rather than away from the user. Furthermore, the guide is not portable but must be fastened to the table while a workpiece must have a predetermined thickness matching a mounting spacer. There is no self contained guide for aligning the workpiece with the saw blade.
Several references teach a single track and follower arrangement in which a relatively long track engages a relatively short follower that must remain within the longitudinal boundaries of the track. Such arrangements have a limited range of motion compared to a bidirectional dual track arrangement.
One single track arrangement is disclosed in U.S. Pat. No. 3,454,056 to Pahlck. In this arrangement the guide pivots out of the way at the end of the limited travel distance to permit additional cutting motion. However, the additional cutting motion is necessarily unguided. In addition, the guide is secured to the relatively short slide bar or track by four wheels which engage close fitting, mating side grooves on either side of the slide bar. This close fitting relationship over a considerable area increases the danger of clogging from sawdust after extended use.
U.S. Pat. No. 3,045,724 to Mitchel discloses another single track and follower arrangement. In this instance the track is secured to a workpiece guide member and the follower is secured to a saw. Two spaced apart sets of 3 ball bearings each are secured by a race and mount the follower to the track. While the ball bearings make a dual line contact with the track, they make an accurate contact with the follower which invites clogging from accumulations of sawdust.
U.S. Pat. No. 2,735,455 to Forsberg discloses another single track and follower arrangement. In this arrangement the track comprises a longitudinally extending vertical wall and the saw is fitted on the side thereof with an inverted U-shaped follower which slidingly engages the vertical track wall. An intended C-clamp mounting to a workpiece securely limits the convenience of using the guide.
Another single track and follower arrangement is taught by U.S. Pat. No. 4,023,273 to Treleaven. In this arrangement the saw travels longitudinally between two laterally spaced track defining side members. The follower is secured to the two side tracks by relatively wide rollers which matingly engage close fitting, U-shaped tracks. The arrangement is thus susceptible to clogging from accumulations of sawdust.
U.S. Pat. No. 3,903,774 to Stinson teaches an arrangement in which the follower is secured to a fairly short track by a sliding tongue and groove arrangement. The guide member engages only the back edge of the workpiece.
Still another track and follower arrangement is taught by U.S. Pat. No. 2,942,633 to King. This arrangement uses a slide bar track which is inconveniently clamped to the workpiece and an invert U-shaped follower which fits over the track and fastens to the saw. The follower slideably engages the track and is readily lifted off the track. The saw is raised a considerable distance above the workpiece.
U.S. Pat. No. 3,869,951 to Litwin teaches still another track and follower arrangement in which the follower slidingly engages the track. The unadjustable guide engages both back and top surfaces of the workpiece but the saw is positioned above the track and follower and hence in vertically spaced relationship to the workpiece.
Miter box arrangements such as those taught by U.S. Pat. No. 335,738 to Booyer or U.S. Pat. No. 4,315,494 to DePlacido offer the advantage of precision cutting but not the convenience of a truly portable saw guide.